Fiber-optics equipment supplier BTI Photonic Systems said Monday it received $12 million from an undisclosed U.S. private equity investor – another sign that the beleaguered communications industry is rebounding.

The investment, which brings the Ottawa-based BTI’s tally to $48 million, comes on the heels of a whopping $225 million venture capital investment in newcomer Zayo Bandwidth, a Louisville, Colorado, fiber-optic services firm. (see Zayo Feasts on $225M Fiber Bankroll)

BTI makes products that allow telephone and cable firms to get more bandwidth out of their already installed fiber-optic lines without digging up the ground to add new lines.

“We’ve seen the demand cranking up in the last year or so and we see the demand coming from the popularity of video, social networking, and file-sharing,” said Lance Laking, CEO of BTI. “The other strong demand driver is the popularity of mobile devices and all of the new video and other applications being carried on mobile networks.”

While overall capital spending by carriers on their networks has remained relatively flat, one of the main growth areas has been fiber-optics. According a recent report from Ovum-RHK, global spending on optical equipment grew to $3.5 billion in the second quarter, representing a 20 percent increase from a year ago. (see Fiber Diet for Telecom)

The two largest U.S. carriers, AT&T and Verizon, were responsible for a lot of that growth, according to the report. Both carriers are spending billions of dollars to bring fiber optics to the American home as the carriers attempt to distribute TV, video, and other high-bandwidth services to consumers.

Traffic generated on mobile networks are transferred onto wireline networks that were once exclusively copper networks, but increasingly those networks are being replaced by fiber-optic lines.

BTI is one of a handful of fiber-optic gear suppliers that survived telecom’s nuclear winter in the late 1990s and early 2000s, when VCs lost billions on the projected bandwidth boom that never materialized.

The company’s investors include Vengrowth Private Equity Partners, BDC Venture Capital, GrowthWorks Capital, Kodiak Venture Partners, Primaxis Technology Ventures, and Lucent Venture Partners.